System-managed storage (SMS) refers to applications or programs that enable an operating system to take over many of the tasks of managing storage, including tasks that were previously performed manually by storage administrators. When configuring an SMS application, a storage administrator may define classes of storage and rules designating how data sets are allocated to these classes of storage. Once the SMS application is properly configured, the SMS application may automatically perform tasks such as allocating data sets to appropriate storage volumes or storage groups, backing up the data sets, managing space in the storage volumes or storage groups, and migrating older data sets to less expensive forms of storage.
SMS applications are important to keep storage costs down and ensure that storage is used efficiently. The costs of storage may include not only the initial cost to purchase the storage, but also costs of electricity to operate the storage, facilities to house the store, and personnel to install, monitor, and/or manage the storage. Although removable media such as optical and tape storage may cost less per megabyte than other types of storage, this type of media may require additional time and resources to locate, retrieve, and mount. Considering all the costs, SMS applications play an important role in controlling and managing storage so a business can grow and expand in a profitable manner.
While system managed storage takes away much of the users' responsibility for volume level space management, there are some situations in which a user error or improper monitoring of the system may result in insufficient storage space to complete an input/output (I/O) request. For example, a user may request a large number of recall jobs, exhausting the storage space within a storage group. A user error such as this can lead to a storage system outage, thus preventing critical data sets from being able to extend. The inability to extend critical data sets may have high monetary impacts on the user's business. For example, if the critical data sets include stock market records, every second the storage system is offline may equate to a loss of thousands of dollars. Accordingly, it is important to provide safeguards from a user error that may prevent critical data sets from extending in a storage group.